The present invention relates to footwear construction, and more particularly to a footwear construction in which the sole is attached to the upper by a welt.
A variety of different sole constructions are used by the footwear industry. For the most part, each sole construction has characteristics that make it particularly well-suited for specific applications. For example, some sole constructions are selected for their durability, others for their flexibility and comfort, while still others are selected for their aesthetic appeal. One particularly popular type of sole construction is referred to as a welt construction. Welt constructions are popular because they are durable and are aesthetically desirable. There are a variety of different types of welt constructions, but in each construction a "welt," for example, a strip of material such as leather or hard rubber, is used to intersecure the sole and the upper. FIG. 1 is an exploded sectional view of a conventional welt construction. This construction includes a welt 150 that interconnects an upper 158 and a sole 172. The welt 150 includes a base portion 152 with an upwardly extending rib 154 located toward the center of the base portion and a downwardly extending rib 156 located at the inner edge of the base portion 152. The sole 172 includes an insole 160, a midsole 168, and an outsole 170. The insole 172 includes a downwardly extending rib 164 that is used in interconnecting the insole 160, upper 158 and welt 150.
Assembly of this construction involves a number of common steps. First, the elements of the upper 158 are cut from the desired material and fit together (typically by sewing). The fitted upper 158 is then wrapped tightly around a foot-shaped form, or last, and secured to the insole 160 by stapling, stitching, or otherwise fastening it to the insole rib 164. This step gives the upper 158 the desired shape and is commonly referred to as lasting. Once lasted, the welt 150 is stitched or stapled to the upper 158 and insole 160 by stitches or staples that extend through the inner welt rib 156, the bottom periphery of the upper 158, and the insole rib 164. The midsole 168 is stitched, stapled or otherwise secured to the bottom of the upper/insole assembly. Typically, the midsole 168 is attached to the upper/insole assembly by stitching that extends through the base portion 152 of the welt 150 and the midsole 168. Afterwards, the outsole 170 is secured to the bottom of midsole 168, typically by cement or other adhesives. Although this construction is durable and aesthetically appealing, it is a relatively heavy construction and it does not provide the flexibility of other constructions.
In an effort to improve the flexibility and reduce the weight of the sole, a variety of sole constructions have been developed which incorporate polyurethane. For example, some footwear manufacturers currently sell footwear that incorporates a solid polyurethane outsole. Typically, the polyurethane outsole is either directly attached to the upper or it is attached to a midsole that is in turn attached to the upper. Polyurethane is a relatively soft material and it is not as wear-resistant as many other outsole materials, such as leather and rubber. Also, polyurethane has relatively low tear-resistant characteristics. As a result, it does not hold a stitch or staple well, and is consequently not well suited for use in a welted construction.
In an effort to overcome these problems, a number of attempts have been made to enclose the polyurethane in a shell. The shell is relatively wear resistant and it forms the wear surface of the sole. One such construction includes a rubber shell that is filled with polyurethane. The shell is cemented to the upper in a conventional manner. Although this construction provides the improved comfort and weight characteristics of polyurethane, it fails to provide the durability and aesthetic benefits of a welt construction.